I am using sqlite3 in a linux machine and I am getting the database without username and password. Can I set a username and password for the same?
SQLite doesn't have a concept of username/password. It's just a single file based database.
However, on Unix you can protect your database from other users on the same machine by setting the permissions of the database file itself.
e.g. Allow only owner access
chmod 700 /path/to/sqlitedb
If it's used in a simple web application then the web application will provide the control.